[Madlug] i lost root!

Mark Tinberg tinberg at securepipe.com
Wed Aug 1 18:38:01 CDT 2001


On Wed, 1 Aug 2001, Nori Heikkinen wrote:

> break the sequence and give me a prompt?  normally i'd just play
> around with it, but i hate bringing the whole system down cold over
> and over just to play around.

You should be able to give it the three-finger-salute (CTRL-ALT-DEL) from
the console and initiate a reboot without logging in.  This should be
configured in your /etc/inittab.

Other useful feature when you are having serious hardware problems.

Magic SysReq: linux/Documentation/sysrq.txt

*  How do I enable the magic SysRQ key?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You need to say "yes" to 'Magic SysRq key (CONFIG_MAGIC_SYSRQ)' when
configuring the kernel. This option is only available in 2.1.x or later
kernels. Once you boot the new kernel, you need to enable it manually
using following command:

         echo "1" > /proc/sys/kernel/sysrq

*  How do I use the magic SysRQ key?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On x86   - You press the key combo 'ALT-SysRQ-<command key>'. Note - Some
           (older?) may not have a key labeled 'SysRQ'. The 'SysRQ' key is
           also known as the 'Print Screen' key.

On SPARC - You press 'ALT-STOP-<command key>', I believe.

On the serial console (PC style standard serial ports only) -
           You send a BREAK, then within 5 seconds a command key. Sending
           BREAK twice is interpreted as a normal BREAK.

On PowerPC - Press 'ALT - Print Screen (or F13) - <command key>,
             Print Screen (or F13) - <command key> may suffice.

On other - If you know of the key combos for other architectures, please
           let me know so I can add them to this section.

*  What are the 'command' keys?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
'r'     - Turns off keyboard raw mode and sets it to XLATE.

'k' - Secure Access Key (SAK) Kills all programs on the current virtual
          console. NOTE: See important comments below in SAK section.

'b'     - Will immediately reboot the system without syncing or unmounting
          your disks.

'o'     - Will shut your system off (if configured and supported).

's'     - Will attempt to sync all mounted filesystems.

'u'     - Will attempt to remount all mounted filesystems read-only.

'p'     - Will dump the current registers and flags to your console.

't'     - Will dump a list of current tasks and their information to your
          console.

'm'     - Will dump current memory info to your console.

'0'-'9' - Sets the console log level, controlling which kernel messages
          will be printed to your console. ('0', for example would make
          it so that only emergency messages like PANICs or OOPSes would
          make it to your console.)

'e'     - Send a SIGTERM to all processes, except for init.

'i'     - Send a SIGKILL to all processes, except for init.

'l'     - Send a SIGKILL to all processes, INCLUDING init. (Your system
          will be non-functional after this.)

'h'     - Will display help ( actually any other key than those listed
          above will display help. but 'h' is easy to remember :-)

-- 
Mark Tinberg <MTinberg at securepipe.com>
Network Security Engineer
SecurePipe, Inc. -- Managed Network Security Services
Remember:  Wherever you go, there you are!




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